Studies on the cellular response to heat shock and other physiological stresses have identified important families of proteins that are involved not only in cellular protection against these aggressions, but also in essential biochemical and immunological processes in unstressed cells. The heat shock proteins include, but are not limited to hsp70, hsp90, gp96, and hsp100; these hsp families accomplish different kinds of chaperoning functions. For example, hsp70, located in the cell cytoplasm, nucleus, mitochondria, or endoplasmic reticulum, (Lindquist, S., et al., 1988, Ann. Rev. Genetics 22:631-677) are involved in the presentation of antigens to the cells of the immune system, and are also involved in the transfer, folding and assembly of proteins in normal cells. Similarly, Hsp90 located in the cytosol are involved in chaperoning and gp96 present in the endoplasmic reticulum are involved in antigen presentation (Srivastava, P. K., et al., 1991, Curr. Topics in Microbiology & Immun. 167:109-123).
2.1. Immunotherapy
In modern medicine, immunotherapy or vaccination has virtually eradicated diseases such as polio, tetanus, tuberculosis, chicken pox, measles, hepatitis, etc. The approach using vaccinations has exploited the ability of the immune system to prevent infectious diseases. Such vaccination with non-live materials such as proteins generally leads to an antibody response or CD4+ helper T cell response. Raychaudhuri, S. and Morrow, W. J. W., 1993, Immunology Today, 14:344-348. On the other hand, vaccination or infection with live materials such as live cells or infectious viruses generally leads to a CD8+ cytotoxic T-lymphocyte (CTL) response. A CTL response is crucial for protection against cancers, infectious viruses and bacteria. This poses a practical problem, for, the only way to achieve a CTL response is to use live agents which are themselves pathogenic. The problem is generally circumvented by using attenuated viral and bacterial strains or by killing whole cells which can be used for vaccination. These strategies have worked well but the use of attenuated strains always carries the risk that the attenuated agent may recombine genetically with host DNA and turn into a virulent strain. Thus, there is need for methods which can lead to CD8+ CTL response by vaccination with non-live materials such as proteins in a specific manner.
The era of tumor immunology began with experiments by Prehn and Main, who showed that antigens on the methylcholanthrene (MCA)-induced sarcomas were tumor specific in that transplantation assays could not detect these antigens in normal tissue of the mice (Prehn, R. T., et al., 1957, J. Natl. Cancer Inst. 18:769-778). This notion was confirmed by further experiments demonstrating that tumor specific resistance against MCA-induced tumors can be elicited in the autochthonous host, that is, the mouse in which the tumor originated (Klein, G., et al., 1960, Cancer Res. 20:1561-1572).
In subsequent studies, tumor specific antigens were also found on tumors induced with other chemical or physical carcinogens or on spontaneous tumors (Kripke, M. L., 1974, J. Natl. Cancer Inst. 53:1333-1336; Vaage, J., 1968, Cancer Res. 28:2477-2483; Carswell, E.A., et al., 1970, J. Natl. Cancer Inst. 44:1281-1288). Since these studies used protective immunity against the growth of transplanted tumors as the criterion for tumor specific antigens, these antigens are also commonly referred to as "tumor specific transplantation antigens" or "tumor specific rejection antigens." Several factors can greatly influence the immunogenicity of the tumor induced, including, for example, the specific type of carcinogen involved, immunocompetence of the host and latency period (Old, L. J., et al., 1962, Ann. N.Y. Acad. Sci. 101:80-106; Bartlett, G. L., 1972, J. Natl. Cancer Inst. 49:493-504).
Most, if not all, carcinogens are mutagens which may cause mutation, leading to the expression of tumor specific antigens (Ames, B. N., 1979, Science 204:587-593; Weisburger, J. H., et al., 1981, Science 214:401-407). Some carcinogens are immunosuppressive (Malmgren, R. A., et al., 1952, Proc. Soc. Exp. Biol. Med. 79:484-488). Experimental evidence suggests that there is a constant inverse correlation between immunogenicity of a tumor and latency period (time between exposure to carcinogen and tumor appearance) (Old, L. J., et al., 1962, Ann. N.Y. Acad. Sci. 101:80-106; and Bartlett, G. L., 1972, J. Natl. Cancer Inst. 49:493-504). Other studies have revealed the existence of tumor specific antigens that do not lead to rejection, but, nevertheless, can potentially stimulate specific immune responses (Roitt, I., Brostoff, J and Male, D., 1993, Immunology, 3rd ed., Mosby, St. Louis, pp. 17.1-17.12).
2.2. Tumor-Specific Immunogenicities of Heat Shock/Stress Proteins hsp70, hsp90 and gp96
Srivastava et al. demonstrated immune response to methylcholanthrene-induced sarcomas of inbred mice (1988, Immunol. Today 9:78-83). In these studies it was found that the molecules responsible for the individually distinct immunogenicity of these tumors were identified as cell-surface glycoproteins of 96kDa (gp96) and intracellular proteins of 84 to 86kDa (Srivastava, P. K., et al., 1986, Proc. Natl. Acad. Sci. USA 83:3407-3411; Ullrich, S. J., et al., 1986, Proc. Natl. Acad. Sci. USA 83:3121-3125. Immunization of mice with gp96 or p84/86 isolated from a particular tumor rendered the mice immune to that particular tumor, but not to antigenically distinct tumors. Isolation and characterization of genes encoding gp96 and p84/86 revealed significant homology between them, and showed that gp96 and p84/86 were, respectively, the endoplasmic reticular and cytosolic counterparts of the same heat shock proteins (Srivastava, P. K., et al., 1988, Immunogenetics 28:205-207; Srivastava, P. K., et al., 1991, Curr. Top. Microbiol. Immunol. 167:109-123). Further, hsp70 was shown to elicit immunity to the tumor from which it was isolated but not to antigenically distinct tumors. However, hsp70 depleted of peptides was found to lose its immunogenic activity (Udono, M., and Srivastava, P. K., 1993, J. Exp. Med. 178:1391-1396). These observations suggested that the heat shock proteins are not immunogenic per se, but are carriers of antigenic peptides that elicit specific immunity to cancers (Srivastava, P. K., 1993, Adv. Cancer Res. 62:153-177).
2.3. Pathobiology of Cancer
Cancer is characterized primarily by an increase in the number of abnormal cells derived from a given normal tissue, invasion of adjacent tissues by these abnormal cells, and lymphatic or blood-borne spread of malignant cells to regional lymph nodes and to distant sites (metastasis). Clinical data and molecular biologic studies indicate that cancer is a multistep process that begins with minor preneoplastic changes, which may under certain conditions progress to neoplasia.
Pre-malignant abnormal cell growth is exemplified by hyperplasia, metaplasia, or most particularly, dysplasia (for review of such abnormal growth conditions, see Robbins and Angell, 1976, Basic Pathology, 2d Ed., W. B. Saunders Co., Philadelphia, pp. 68-79.) Hyperplasia is a form of controlled cell proliferation involving an increase in cell number in a tissue or organ, without significant alteration in structure or function. As but one example, endometrial hyperplasia often precedes endometrial cancer. Metaplasia is a form of controlled cell growth in which one type of adult or fully differentiated cell substitutes for another type of adult cell. Metaplasia can occur in epithelial or connective tissue cells. Atypical metaplasia involves a somewhat disorderly metaplastic epithelium. Dysplasia is frequently a forerunner of cancer, and is found mainly in the epithelia; it is the most disorderly form of non-neoplastic cell growth, involving a loss in individual cell uniformity and in the architectural orientation of cells. Dysplastic cells often have abnormally large, deeply stained nuclei, and exhibit pleomorphism. Dysplasia characteristically occurs where there exists chronic irritation or inflammation, and is often found in the cervix, respiratory passages, oral cavity, and gall bladder.
The neoplastic lesion may evolve clonally and develop an increasing capacity for invasion, growth, metastasis, and heterogeneity, especially under conditions in which the neoplastic cells escape the host's immune surveillance (Roitt, I., Brostoff, J and Kale, D., 1993, Immunology, 3rd ed., Mosby, St. Louis, pps. 17.1-17.12).